This invention relates to a fuel injection valve in which a fully lifted amount of a valve element is adjustable.
In general, the fuel injection valve includes an elongated sleeve-like body and a valve seat member fixedly received in a lower end portion of the body. The valve seat member includes a guide hole extending axially, an injection port disposed at a lower end thereof, and a valve seat for intercommunicating the injection port and the guide hole. A needle-like valve element is slidably received in the guide hole of the valve seat member.
The valve element is lifted from a position where a valve portion formed on its lower end sits on the valve seat to a position where its upper end is brought into abutment with a stopper, so that fuel is injected from the injection port. The fully lifted amount of the valve element is one of the factors for determining an amount of injection of fuel.
Japanese Laid-Open Patent Application No. Hei 5-501748 (corresponding to U.S. Pat. No. 5,263,648 and EPC Pat. No. 497931B1) discloses a fuel injection valve in which the fully lifted amount of the valve element is adjustable. This fuel injection valve has a nozzle plate welded to a lower end face of a valve seat member. The nozzle plate has an opening formed in its central area and communicating with an injection port of the valve seat member. A peripheral edge portion of the nozzle plate is bent and formed into a sleeve-like configuration. This peripheral edge portion is welded to an inner peripheral surface of a lower end portion of a body. As a consequence, the valve seat member is not secured directly to the body but connected to the body through the nozzle plate.
In the fuel injection valve taught by the above publication, the position of the valve seat member is gradually finely adjusted upwardly relative to the body by finely deforming the nozzle plate with the use of a jig. By doing this, the fully lifted amount of the valve element is gradually finely changed. Each time the fine adjustment is made, fuel is injected and the amount of injection of the fuel is measured. When a desired amount of injection of fuel is obtained, the adjusting work is finished.
In the above-mentioned fuel injection valve, the fully lifted amount of the valve element can be adjusted with ease, simply by deforming the nozzle plate. Further, since the peripheral edge portion of the nozzle plate is welded to the inner peripheral surface of the body, there can be prevented the fuel from leaking from a gap between the body and the valve member and therefore, there is no need of a provision of a seal member such as an O-ring
However, the above conventional fuel injection valve has the following shortcomings. A shock occurs to the valve element each time the valve element sits on the valve seat. Since the valve seat member is not secured directly to the body, this shock is applied to the nozzle plate. The nozzle plate is subjected to aging deformation by repeated shocks. Accordingly, the position of the valve seat member is gradually lowered relative to the body. As a consequence, the fully lifted amount of the valve element is increased, little by little, with the passage of time.